Two Bronto aerial fire trucks equipped with long-reaching mechanical ladders and remotely-operated water jet systems were sent from Napier and Palmerston North to help contain the fire.
The intense heat activated the internal sprinkler system of a nearby factory.
Earlier, a firefighter was taken to Hawke's Bay Hospital suffering from heat exhaustion.
Five remaining crews were dampening the area and some deep-seated fire in packaging material was being turned over by diggers, he said.
Two fire inspectors have arrived at the site and were conducting interviews and carrying out a scene investigation.
It was too early to say whether the fire was suspicious, said Mr Hall.
He expected firefighters to remain at the site for the rest of the day and probably through until tomorrow.
Residents from neighbouring houses were initially evacuated but have since been allowed to return home.
Hastings police sergeant Bryan Smith said an evacuation plan was in place for nearby residents but was not needed.
It is understood to be the third fire to damage the plant in the past year.
Most recently, a processing plant within the factory was damaged in a blaze in October.
